This invention relates to a television camera for acquiring video signals having a broad dynamic range. More particularly, this invention relates to an iris control method and apparatus for a television camera for controlling an iris of a lens in response to video signals picked up by the television camera, and a television camera using the same.
A television camera for acquiring video signals having a broad dynamic range is heretofore known which uses a solid state image pickup device capable of outputting on a time division basis a long-time exposure video signal obtained by photoelectrically converting long-time exposing light beams and a short-time exposure video signal obtained by photoelectrically converting short-time exposing light beams. A lens having an automatic iris control function, that is, an automatic iris lens system is used for this television camera. The automatic iris lens is realized by a DC voltage control system such as a galvanometer system.
Next, a prior art technology of a conventional broad dynamic range television camera using an automatic iris lens system, in which the iris is controlled upon inputting of video signals, will be explained with reference to FIG. 1 showing its construction. In the drawing, an automatic iris lens 17 condenses light beams from an object. The light beams are then incident into a solid state image pickup device (charge-coupled device: CCD) 18. The CCD 18 alternately outputs short-time exposure video signals obtained by exposing the light beams for short exposing period, such as 1/2,000 seconds, for example, and long-time exposure video signals obtained by exposing the light beams for a longer exposing period than the short exposing period to the short-time exposure video signals, such as about 1/60 seconds. It will be assumed hereby that time-base compressed long-time exposure video signals for one horizontal scanning and time-base compressed short-time exposure video signals for one horizontal scanning are outputted within one horizontal scanning period. A CDS (correlation double sampling) circuit 19 samples and holds the video signals outputted from the CCD 18. An AGC (automatic gain control) circuit 20 conducts automatic gain control of the video signals so sampled and held to signals having a predetermined level. Further, an A/D (analog-to-digital) converter 21 converts the video signals, which are analog video signals into digital video signals.
The video signals sampled and held by the CDS circuit 19 are further inputted as an iris control signal to an automatic iris lens 17. The automatic iris lens 17 executes iris control in accordance with the iris control signal so inputted.
On the other hand, the digital video signals outputted from the A/D converter 21 are inputted to a synchronization circuit 22, where they are separated into the long-time exposure video signals and the short-time exposure video signals. Both of these signals are time-wise extended to signals having a length of one horizontal scanning period. The synchronization circuit 22 synchronizes the extended long-time exposure video signals and the extended short-time exposure video signals so that they can be outputted simultaneously.
After synchronized in the synchronization circuit 22, the synchronized long-time exposure video signals and the synchronized short-time exposure video signals are inputted to a synthesis circuit 31, where they are synthesized. The resulting video signals of the synthesizing are inputted to a video signal processing circuit 32. After executing a predetermined video signal processing such as gamma correction, enhancer processing, white balance processing, and so forth, for the input video signal, the video signal processing circuit 32 outputs the signal to a post-stage circuit (not shown).
A microcomputer (CPU) 33 controls the operations of the AGC circuit 20, the video signal processing circuit 32 and the synthesis circuit 31, and incorporates software for executing automatic gain control processing, white balance processing, synthesis processing, and so forth.